Thread: ER32 collet adaptor for Hercus 260

Originally Posted by nadroj

Unlike some other lathes that have close-fitting registers

Both chucks that came with my 260 have tight fitting registers. The one on the four jaw being slightly closer than the three jaw.
CORRECTION I must have never checked that. Now that I have actually measured things it would seem it's not that tight. The land on the spindle measures 44.4mm and the closest fitting chuck (the 4 jaw) measures 44.65mm. My apologies.

John

Originally Posted by nadroj

By register, I take that to mean the flat face that the chuck butts up against.

The flat face on the shoulder on the spindle and the flat face at the rear of the chuck butt up against each other and rotational movement comes to a stop, unless one strips the threads or snaps the spindle nose off etc.

How would just tightening up against it make the chuck centralised?

Mmmm. By implication, slight differences in the machining on spindle shoulders on multiple spindles and slight differences in the machining on the rear face of chucks on multiple chucks will mean amplified differences in the accuracy of fit of different chucks on different spindles, and non-interchangeability accuracy-wise.

A thread cannot work without clearance. (i.e. After it tightens up, if it was a little loose to begin with while turning the chuck onto the spindle - there may be only one inter-touching helical face of the two flanks of the Vs of the two thread grooves.)

Something must be pulling the chuck into alignment despite the clearance. Is there doubt that it's the angled flank of the thread?
I'm assuming the same pitch on both the spindle and chuck, of course.


Jordan

I think the alignment will vary from chuck to chuck, from spindle to spindle, and from manufacturer to manufacturer, but the original chuck and spindle sold with/fitted to the lathe will be pretty good matches for each other.

Originally Posted by nadroj

By register, I take that to mean the flat face that the chuck butts up against.
How would just tightening up against it make the chuck centralised?
A thread cannot work without clearance.
Something must be pulling the chuck into alignment despite the clearance. Is there doubt that it's the angled flank of the thread?
I'm assuming the same pitch on both the spindle and chuck, of course.

Jordan

The resister doesn't centralise the chuck, and as I said, that is done by the thread. However the pitch itself (ie the tpi) won't affect the centralisation, only that it needs to not bind. You can cut a very loose, or have a worn, thread for example, and that won't mean the chuck will be as proportionately inaccurate, just so long as it is still accurately concentric. At the moment at which the register contacts the thread, it is no longer a "thread" and instead can be thought of as a type of wedge that uses its flanks to lock the chuck in place against that register. So long as it locks in place each time at the same location, and the front of the chuck is machined on that same machine, you should be good to go.

Hopefully that makes sense and is fine in theory. In practice however it would be bad form to expect good results cutting a bodgy thread. Large clearances (regardless of why they're there) aren't generally conducive to tight tolerances. The chances are that something will smell rotten in the land of chucks if you tried to cut a completely wrong thread pitch with massive clearances so it didn't bind, and expected it to register in exactly the same place each time. Instead of tightening along the length of the thread, you'd be tightening along only a very small portion of it, and I doubt that would finish p as a happy ending. I can't say it can't be done, but I wouldn't personally try it. I will personally try for a particularly good class fit on these threads when I do them for that reason.

I guess the bottom line to what I'm saying is that if you're forced to make a decision on financial grounds between transposing gears and an ER32 chuck, despite my enthusiasm for the chuck, I would probably suggest you go for the gears. Even if you don't do a lot of single point thread cutting. Until then you really only have half a thread cutting lathe. You can always use the gears to make the chuck, and they're not hard to make, but you sure as heck can't use the chuck to make the gears (though they're also not hard to make and I've made a stack of them too, they just require completely different gear not everyone has).

OK, I think I'm following Pete now, thanks.
But, why would anyone try to cut a wrong thread, and compensate with a loose fit?
The imperfect results (but very close I'm told) that can be got from the 260's transposing gears might be enough to prevent good centring on the spindle. After all, it's more important than just a nut for a bolt. So, should one get a 127 tooth gear to make backplates and collet chucks? Would one fit, even with the cover removed?

Jordan

Just had a go myself today. I went to someone with the 960B to cut the internal thread.
Its 1-3/4 8tpi. The shoulder is 1-3/4" x 1/4"

So far so good.

Regards,
Trong

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Its quite nice but boring to watch...

Originally Posted by nadroj

OK, I think I'm following Pete now, thanks.
But, why would anyone try to cut a wrong thread, and compensate with a loose fit?
The imperfect results (but very close I'm told) that can be got from the 260's transposing gears might be enough to prevent good centring on the spindle. After all, it's more important than just a nut for a bolt. So, should one get a 127 tooth gear to make backplates and collet chucks? Would one fit, even with the cover removed?

Jordan

The reason somebody might try to cut an incorrect thread is if they had a metric lathe and wanted to cut an imperial thread. On short threads you can sometimes use a metric thread instead of an imperial and visa versa. That's why I included the thread chart of imperial v metric threads. In this case however there isn't a close metric thread. But it's always worth checking, as if you have other gears, it's possible to come up with threads that aren't in the gearbox chart. You just need to manually work out the gear ratios. For example I sometimes need to cut Schaublin threads and they are 1.666667 mm pitch!

No as I've said, the thread pitch doesn't affect centring, only whether the thread can actually be done up. The error from the imperfect translation is so small it won't affect anything unless you're using the thread for a leadscrew or something where the actual thread pitch must meet a specific tolerance. It's hard to imagine a female thread long enough to actually bind due to the error.

Originally Posted by Pete F

On short threads you can sometimes use a metric thread instead of an imperial and visa versa.

It doesn't have to be a standard metric thread on a metric lathe necessarily (or vice versa) ... you can use any combination of change gears and/or QC gear ratios to get very very close to the desired imperial thread on a metric lathe and vice versa.
You'd be surprised just how often you can less than just a few % error with very limited change gears.

Originally Posted by Vernonv

You'd be surprised just how often you can less than just a few % error with very limited change gears.

Yes, that's often reported to be the case and I'm sure it's usable for lots of jobs.
However, for critical parts like leadscrews and spindle threads, I think it's probably worthwhile to get as perfect as possible, which involves a 127 tooth transposing gear, or use a lathe with native standard the same as the thread you want.

The Hercus 260 AM lists 8TPI as one of the imperial pitches you can get with its 63/64 transposing gears. Is it good enough?

Originally Posted by nadroj

However, for critical parts like leadscrews and spindle threads, I think it's probably worthwhile to get as perfect as possible ...

I would agree that for a leadscrew, you would want a perfect thread, but for most other applications, and certainly even a spindle thread, if you can get within a few % error, you'd not have an issue.

Originally Posted by nadroj

However, for critical parts like leadscrews and spindle threads, I think it's probably worthwhile to get as perfect as possible, which involves a 127 tooth transposing gear, or use a lathe with native standard the same as the thread you want.

I agree with this assessment.
If you are using the thread face pressure to centre the chuck on the spindle, the pitch needs to be as close to perfect as possible, or else the closing force as the thread is tightened will not be even around the whole diameter of the thread(s). This will cause a slight skewing of the chuck, or slight sideways movement of the chuck on the spindle as the thread faces try to even the pressure.
Think of the thread as a circular wedge, and unroll it. The variation in the pitch (wedge angle) will create a skewing motion as the wedge is tightened. On a thread this will cause unpredictable non-centralised movement.

Andrew.

Originally Posted by Vernonv

It doesn't have to be a standard metric thread on a metric lathe necessarily (or vice versa) ... you can use any combination of change gears and/or QC gear ratios to get very very close to the desired imperial thread on a metric lathe and vice versa.
You'd be surprised just how often you can less than just a few % error with very limited change gears.

Well yes, that's why I provided a link with a whole table of threads where the metric v imperial and imperial v metric threads were listed and I said that table is actually laminated and posted in my workshop. I also mentioned how I cut 1.667 mm pitch threads with additional gears. So no, having specifically mentioned that, I wouldn't be surprised.

Yes, that's often reported to be the case and I'm sure it's usable for lots of jobs.
However, for critical parts like leadscrews and spindle threads, I think it's probably worthwhile to get as perfect as possible, which involves a 127 tooth transposing gear, or use a lathe with native standard the same as the thread you want.

The Hercus 260 AM lists 8TPI as one of the imperial pitches you can get with its 63/64 transposing gears. Is it good enough?

Jordan, with all due respect, I have explained 3 times now that the thread pitch does not affect the accuracy, and the actual pitch is NOT critical for this purpose. The concentricity of the thread is somewhat more important (and even that doesn't really matter much if it's used on the same lathe, as outlined below), but concentricity is not the thread's pitch. I'm not entirely sure why you keep asking the same question and insisting it is. While 127 is the smallest gear that will give a mathematically perfect ratio, many lathe manufacturers, including Hercus with their 260, don't use it, and the error is extremely small. For threads of typical length, for all intents and purposes it's immeasurable. Now if you were to want to cut a whole leadscrew, that's a different matter, and you'd probably want a perfect translation, but for this purpose it's more than accurate enough.

This is not theory, and Andrew I'm sorry, but that is simply not true. I put up photographs and a description of my own ER32 chuck. It's a very accurate chuck and was made on my own (metric) 260. It's a very common project to do, it's not a particularly difficult project, but I feel it's very satisfying, and I honestly don't understand what the issue is here. Thousands of these chucks would have been made around the world on metric lathes of different manufacturers with imperial spindle noses.

The fact that the working ER32 taper is turned on the lathe on which the chuck will be used means that, with appropriate care, very accurate results can be achieved. The only consideration is that the chuck repeats properly when mounted. Even if the thread was so far out that it was skewing the chuck off (and it won't be with these minuscule errors), it is immaterial, as it will still repeat just fine. After the thread is cut, the chuck is then reversed and the working taper cut, it's the latter where the actual accuracy comes from, not at the spindle end. That just needs to repeat, and Bob's your uncle.

Sorry to annoy you Pete. I guess I'm trying to get to the theory behind it, although I believe what you've said about your experiences.
Sure enough, if you make and use the chuck on the same lathe it would be repeatable, even if there was substantial error at the thread interface.
But what about if I want to buy one of Mal's chucks?
I'm trying to think like Ford, not Rolls-Royce.

If you make your own, you don't need to worry about the accuracy of the threads, the interface, or anything at that end. All you need to worry about is that it repeats correctly. It's why lathe back plates are sold "semi finished" ie with the threads and interface machined but the chuck end of it as cast. That's not done just because the person selling it is lazy, it's so the working end of the backplate (the part that interfaces with the chuck) can be machined on the lathe on which that chuck will be fitted. By machining it on that machine, so long as the interface repeats correctly, that combination will be as accurate as the chuck itself. Having said that, it's good workmanship to machine the spindle end to the best of your ability just to ensure it repeats as well as possible. However if this is just a theoretical exercise, then no, it won't make any difference. What definitely won't make any difference is the minuscule errors in thread pitch that come from using a mathematically imperfect translation gear. The thread is still concentric (and that's the part that matters if you swap to another machine), and threads conform when put under load anyway.

Conversely, the taper end of the chuck is where the accuracy is achieved. You could weld the chuck to end of the spindle with a 10 mm offset for all it matters, once you cut that taper it will be concentric to within the accuracy of the lathe, and even the biggest POS lathe will be VERY accurate in that regard. Getting the correct taper angle just perfect is fiddly, and that will affect the repeatability of the collets. It's probably the hardest part of that job.

Now, if you're buying somebody else's chuck, again you don't need to worry about it. It is what it is, and you will likely never know whether the person making it has done it on a CNC lathe, a 127 tooth translation gear, an imperfect translation gear, or a native leadscrew. It also doesn't matter, just that it's concentric and repeats ok. However in this case you're subjected to the tolerances of the person's machine and your machine, and the tolerances rarely seem to subtract! So if it's purely theory you're concerned about, then ideally you'd skim the taper to get it concentric with your own lathe. In practice however, you're likely to do more harm than good, and it's arguably best left as it is. Mal doesn't sell crap, and it will be quite accurate, even though not quite as accurate as it could theoretically be if it were made on the final machine.

I personally enjoy this type of work, as it requires care and precision, and it's very satisfying to achieve a highly accurate outcome. It's not an especially difficult project however, and is great for skill building as it encompasses quite a few skills. However not everyone has to time or interest to do this type of thing, in which case buy a completed one from Mal and spend the time using it to make other things.

Originally Posted by Hornetb

I've been tempted to get one for the 9" but only now just realised they are out of stock.

I think for $128 they are a pretty good buy. I currently use a MT3 Er32 collet chuck in the headstock but the ability to slide stock right through would be a huge advantage. I use my ER32 collets a lot when machining small stuff. The ability to take things out of the chuck and put them back in is an excellent feature of collet use.

So, if some more 9" ones were to surface again I think I would be interested. These would be infinitely better than any attempt to make one that I would produce.

When the funds become available I will run another batch. What you should be aware of with these threaded models is while they are incredible handy to use (I know as I use them continuously), compared to a taper mounted unit. they have a lot less surface to register on. The accuracy of a taper mounted unit will always be potentially greater to a small degree over the thread mounted one. The only way to overcome this is to cut the er32 taper while mounted on the machine it is to be used on.
These are not for the Micron level perfectionists and while their runout will generally be much better than the average 3 jaw chuck that most people own, they are subject to the condition of spindle register of the machine they are attached to.
I had a member ring me up to complain about the runout on a unit I sold him. Knowing how well these were made I took the time to go and see what was going on. When I examined the lathe it was on, the register was badly distorted, after a quick re-facing of the register it ran out 0.001" compared to the original 0.010". Each machine will have a register of varying accuracy and I can't specify strongly enough the importance of protecting this area of your machine.
For those who feel confident to machine the er32 taper, "Pipeclay" of this forum, will be happy to supply you with a unit complete except for the taper.
Mal